Pancytopenia and marrow infiltration: SAQ

This boy has a trilineage cytopenia with circulating blasts, organomegaly and lymphadenopathy, which is the classic presentation of acute leukaemia with marrow infiltration. The combination of pallor, bruising and fever with a fall in all three lineages is a medical emergency, and the task is to resuscitate the unstable elements first, to confirm the diagnosis rapidly, and to move to definitive therapy in a specialist centre. ^[3]

Question 1 (10 marks)

Outline your immediate assessment, the stabilisation, and the urgent diagnostic pathway for this four-year-old boy. ^[12]

A full-mark answer covers the recognition of the emergency, the resuscitation by the three legs of transfusion, tumour lysis prophylaxis and empiric antibiotics, and the bone marrow diagnostic pathway with the ancillary studies that deliver the named diagnosis. ^[3]

Recognition and the first decision (1 mark). Pancytopenia is a reduction in all three lineages, and the first decision is whether the marrow is empty (failure) or full (infiltration). The circulating blasts with hepatosplenomegaly settle it here: this is a marrow malignancy until proven otherwise, and the boy is moved from an elective workup to an emergency resuscitation. ^[1]

Resuscitation by transfusion (3 marks). Red cells are transfused for symptomatic or rapidly falling anaemia, given slowly in the chronically severely anaemic child to avoid circulatory overload, and all cellular products are irradiated and leucodepleted because a marrow malignancy demands protection against transfusion-associated graft-versus-host disease. Platelets are transfused prophylactically under ten times ten to the nine per litre in the stable child and under twenty in the febrile or bleeding child, and at a higher threshold for active bleeding or before a procedure. The boy is typed and crossed for cytomegalovirus-safe products if he is a transplant candidate. ^[12]

Tumour lysis prophylaxis (3 marks). A bulky or high-turnover tumour carries a risk of the tumour lysis syndrome, which is prevented before the first dose of chemotherapy. Hyperhydration with an isotonic fluid without potassium, started early and run to maintain a high urine output, is the foundation. Rasburicase, a recombinant urate oxidase, is given to the high-risk child to break down the urate already formed, and is far more effective than allopurinol, which only blocks new urate formation. Rasburicase is contraindicated in glucose-6-phosphate dehydrogenase deficiency because it causes haemolysis and methaemoglobinaemia. The potassium, phosphate, calcium, creatinine and urate are measured every four to six hours. ^[12]

Diagnostic pathway (3 marks). Blood cultures are drawn and an empiric antipseudomonal beta-lactam such as piperacillin-tazobactam, ceftazidime or meropenem is given within one hour for the febrile neutropenia. The bone marrow aspirate and trephine biopsy are performed together at the posterior iliac crest, with the aspirate providing cells for morphology, flow cytometry to define the lymphoid lineage, and the molecular studies that drive the modern risk stratification, and the trephine biopsy providing the architecture and the cellularity. The diagnosis of acute lymphoblastic leukaemia rests on the blast morphology and the flow cytometry, and the cytogenetics and molecular panel drive the risk group that shapes the protocol. ^[3]